Emissions Testing Fuel Handling System

Author(s):
Robert Conde - VI Engineering

Industry:
Automotive

Products:
LabVIEW

The Challenge:
Remotely provide rigid temperature, amount, and flow control for fuel dispensing during Federal (EPA) emissions tests for the DaimlerChrysler Proving Grounds. Communicate with and control another remote LabVIEW system designed to dispense specialty fuels. Receive commands from the emissions program to seamlessly execute an emissions test.

The Solution:
Use LabVIEW and National Instruments hardware to remotely monitor and control the fuel dispenser in the room. Communicate using TCP/IP to a separate LabVIEW application for specialty fuel dispensing.

Abstract
The Fueling Bay contains an enclosure (Shed) for the vehicle, which measures the amount of fuel vapor released during vehicle fueling. All electronic equipment must be in a remote location, to avoid igniting vapors. The computer (in the adjoining Control Room) uses the NI serial card to communicate with both the SCXI chassis and FieldPoint modules in a control panel above the Bay. The hardware controls a variety of pneumatic valves that perform the fueling control. To pass the EPA tests, the temperature, flow rate, and dispense amounts must stay within tight, predefined limits during fueling.

Introduction
VI Engineering, Inc., a National Instruments Premier Alliance Member, was contracted by DaimlerChrysler to create control programs for their Emissions Fueling System. The ORVR Fueling Bay (Bay 5) can supply one of several types of fuel to a test vehicle. The system controls the temperature, flow rate, and amount of dispensed fuel. One dispenser pumps fuels from large tanks containing commonly used grades. Another dispenser supplies specialty fuel mixes from a 55-gallon drum in a separate room. Automobiles must be designed to capture fuel vapors released during refueling. Bay 5 is used for the Onboard Refueling Vehicle Recovery test (ORVR), which is mandated by the Environmental Protection Agency (EPA). The ORVR test requires that the fuel remain within a specific temperature and flow rate range while dispensing. Hydrocarbons released into the air during fueling are measured by the Shed enclosure. The results are printed in a report and are submitted to the EPA (for certification vehicles).

System Description
Bay 5 and its bulk fuel conditioning room handle large amounts of hazardous fuel. To prevent the ignition of fumes, the stands are controlled by pneumatic valves. The few electrical components are housed in sealed, explosion-proof casings. The industrial computer is in the Control Room, adjacent to Bay 5. The computer communicates using RS-485 with the control hardware: an SCXI chassis and a FieldPoint network module. This equipment is located in an electrical control panel outside of the fuel conditioning room. The hardware performs the data acquisition and controls variable-position valves.

Bay 5 contains the Shed enclosure and two fuel dispensers. The Shed houses the vehicle being tested; its door has an airtight seal to prevent fuel vapor leakage during an ORVR test. The dispenser nozzle is placed into the vehicle through a boot in the Shed wall, which also provides a seal. A C program developed by DaimlerChrysler controls the Shed; it allows the operator to enter the test parameters and controls the various fans and vapor-analyzing equipment during a test.

The bulk fueling stand has one dispenser that supplies the five most common types of fuel. Heat exchangers warm or cool the fuel, and pneumatic valves control the dispense flow rate. A second dispenser is connected to a two-drum fueling stand in a separate Fueling Bay (Bay 4).  The drums are surrounded with a clamp-on heat exchanger. The system varies the amount of hot and cold glycol that flows into the exchanger until the correct fuel temperature is achieved. A pneumatic flow valve controls the fuel dispense rate. The drum stand can also dispense fuel into Bay 4, for general refueling.

The system can be controlled from the LabVIEW program (for general refueling and status monitoring) or from the Shed program, which also resides on the industrial computer. The Shed program controls the ORVR test and commands the LabVIEW application to prepare and dispense the fuel.

Performance Issues
Both stands contain multiple PID loops to control the temperature and flow rate, and each stand also has numerous valves controlled by digital outputs. Therefore, the system is processing large amounts of information and I/O at high speeds. The original program executed too slowly to perform a valid ORVR test, so the code was rewritten in LabVIEW. The LabVIEW application performs all of the necessary control and communications required for the test.

The SCXI chassis and FieldPoint hardware are located in a remote control panel. The industrial computer in the Control Room communicates with them using a National Instruments AT-485/2 communication card in the industrial computer. The FieldPoint system communicated over a second RS-485 line (to a separate port) to reduce the traffic over the SCXI’s serial line. This was a cost-effective method to provide fast control and data acquisition for the system.

Flexibility
Routine maintenance of the system may change the response of its valves. Calibration screens help maintain consistent performance even when the hardware has changed. These tools also help to troubleshoot hardware problems. The user can adjust each amount, temperature and flow PID from an easy-to-use tuning screen.

Communications
The Bay 5 LabVIEW application communicates with two other programs. It uses text files to rapidly pass setpoints and status information to the Shed program (on the same computer). An operator can use the Shed program to run an ORVR test without entering data into the LabVIEW program. The Shed program receives and displays the current fuel temperature, flow rate, and dispense amount from the LabVIEW program.
The program also uses TCP/IP to communicate with another computer over a network. The other computer runs a LabVIEW application that controls the specialty fuel stands in another room (Bay 4). The status of the drum stand is always displayed on the Bay 5 screen. When the drum dispenser is to be used in Bay 5, it commands the Bay 4 software to condition and dispense the fuel. The drum fuel is easily available from either the Shed program or LabVIEW application.

Conclusion
V I Engineering has developed a control program for the ORVR Fueling Bay at the DaimlerChrysler Proving Grounds. This system supplies a variety of different fuels for emissions test vehicles. The desired fuel temperature, dispense rate, and amount can be entered by the operator on an attractive LabVIEW display, or sent from an independent ORVR test program. The computer remotely controls the system using serial and TCP/IP communications. Large numbers of inputs and outputs are handled quickly by the program to meet the strict requirements of the tests. Using LabVIEW and National Instruments hardware, V I Engineering has produced a system that delivers accurate results with a minimum of operator time.

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